Resolving Heterogeneity in CO2 Uptake Potential in the Greenland Coastal Ocean.

The oceans play a pivotal role in mitigating climate change by sequestering approximately 25% of annually emitted carbon dioxide (CO2). High‐latitude oceans, especially the Arctic continental shelves, emerge as crucial CO2 sinks due to their cold, low saline, and highly productive ecosystems. However, these heterogeneous regions remain inadequately understood, hindering accurate assessments of their carbon dynamics. This study investigates variation in pCO2 levels during peak ice sheet melt, in the Greenland coastal ocean and estimates rates of air‐sea exchange across 6° of latitude. The East and West coast of Greenland displayed distinct regions with unique controlling factors. Though, both coasts represent CO2 sinks in summer. Geographical variation in pCO2 and air‐sea exchange was linked intricately to freshwater export from the Greenland ice sheet and levels of primary production in these ecosystems. Air‐sea exchange of CO2 ranged from 0.23 to −64 mmol m−2 day−1. However, we found that flux estimation faces substantial uncertainties (up to 672%) due to wind product averaging and gas exchange formula selection. Upscaling only heightens this uncertainty leading to wide ranging estimates of Greenland coastal CO2 uptake between −16 and −26 Tg C year−1 (This study, Dai et al., 2022, https://doi.org/10.1146/annurev‐earth‐032320‐090746; Laruelle et al., 2014, https://doi.org/10.1002/2014gb004832). Obtaining a reliable assessment of air‐sea CO2 exchange necessitates data collection across seasons, and, even more so, refinement of the gas transfer velocity estimations in the Arctic coastal zone. Plain Language Summary: The oceans help to limit climate change by absorbing large amounts (1/4) of carbon dioxide (CO2) that is annually emitted to the atmosphere. The majority of oceanic CO2 uptake occurs near the poles due to the special conditions that occur in these regions: namely that there is cold, less salty water, with high quantities of photosynthetic algae in the surface ocean. However, scientists do not completely understand the regional variability of oceanic CO2 uptake, which limits our ability to accurately predict future climate scenarios. This study measured the partial pressure of CO2 in the ocean along East and West Greenland to calculate rates of air‐sea transfer. Air‐sea exchange of CO2 ranged from 0.23 to −64 mmol m−2 day−1 and the controlling factors behind this flux of carbon were wind speed, amount of glacial runoff, and the balance between biologic producers/consumers. However, several wide‐ranging estimates of uptake in the Greenland coastal ocean have been proposed, indicating the need to better understand carbon sequestration variability in this region. Key Points: The Greenland coastal ocean takes up large quantities of carbon dioxide yet displays considerable spatial heterogeneityBiology and freshwater runoff control pCO2 levels to varying degrees in different regionsEstimation of the true flux magnitude is beset by large uncertainties, particularly in polar coastal regions [ABSTRACT FROM AUTHOR]